I was always surprised at the lack of empathy people had towards Melody, a troubled teen coming from a very difficult family background. When you compare it to the strong compassionate feelings people had for other characters like Aden (with the abuse), Geoff & Annie (with their sheltered upbringing) or even Nicole (during the period where she felt nobody care for her), it seems quite odd.
I think a lot of the lack of understanding can be credited to the inconsistencies in writing her, moving her from guest to perm character. If you look back, during her guest stint, people had a great affection for her character, especially when Geoff chose her over Nicole. The cute/naive/innocent relationship that followed & then the slow unravelling of her emotionally abusive background (at the hands of Christine). All of this made people understand, care for & empathise with her character easily. But this was only a short story arc with a guest character & she left.
When they brought her back, they went through too many different phases with her character, in a short space of time & it was confusing. She went from a meek, innocent teen that was entirely controlled by her parents, to a mentally-unstable girl who had visions of a dead Axel, then she was okay again. And finally when she got some freedom, she went down the goodgirl gone bad route. The writers didn't know which route to take with her, so they kept changing lanes, which makes it harder to see the journey her character' going on.
Also watching a goodgirl with high morals, who could be quite judgemental turn bad & carry out bad actions is harder to connect with, then the opposite where a badboy/girl starts to change for the better. Look at how people villified Annie when she had her bad phase (wrongly accusing Aden etc.).
None of these are good enough excuses, or is correct reasoning for not bothering to look below the surface. But they are reasons people might find it hard to undertsand or connect with her. I had a phase where I was starting to get annoyed by Melody & her actions. But I never forgot about her controlled upbringing & all that she's been through. I think the scene where she tells Annie/Ruby "No-one liked the old me, no-one likes the new me, I don't know who i'm meant to be anymore" really helped me understand her & the reasoning behind some of her most recent behaviour. This 'not belonging' or identity crisis is what the writers are trying to show through Melody, but in the transition from guest to perm character, some of her story/journey has gotten confusing & not been explained clearly enough.